1. Field of the Invention
The present invention generally relates to storage area network (SAN) technology. More particularly, the present invention pertains to a method and apparatus for determining the disk array enclosure serial number using SAN topology information for storage arrays.
2. Description of the Related Art
Dynamic Multipathing (DMP) processes (also referred to herein as simply DMP) balance input/output (I/O) across all available paths between a server and array of storage devices within storage systems, to improve performance and availability. The DMP processes used in conjunction with a SAN identify the particular disks (or storage devices) in an array within a storage system. The identity of a particular disk array is known as Disk Array Enclosure Serial Number in a SAN topology. Once known, the DMP can dynamically control routing of I/O traffic to the array with high granularity, i.e., send traffic to specific disk drives. The identification of the disk array enclosure serial number is generally contained in an Array Support Library (ASL) that is provided by the array to the DMP.
Data classification in a SAN is the manual decision making process that identifies data, determines its value to the organization and classifies the data into different categories. Categories may be based on levels of protection needed, performance requirements, frequency of use, and other considerations. Tiered storage facilitates assignment of the different categories of data to different types of storage media in order to reduce total storage cost. Often, enterprise data centers utilize a different storage array for each tier. As an example of tiered storage, tier-1 data such as mission-critical, recently accessed, or top secret files are stored in a tier-1 storage array of expensive and high-quality media, such as double-parity RAIDs (redundant arrays of independent disks). Tier-2 data such as financial, seldom-used, or classified files are stored in a tier-2 storage array of less expensive media in conventional storage area networks SANs. DMP supports a majority of tier-1 storage arrays.
Array Support Library (ASL) is a dynamically loadable library (or shared library) to discover attributes of a disk array. The ASL is invoked during volume manager configuration daemon start up process. The ASL identifies a disk to device discovery layer (DDL) during runtime. The set of ASL is limited as compared to the number of array vendors in the market. The DMP supports a majority of tier-1 storage arrays, but does not support lower level arrays, i.e., certain arrays are certified for use with DMP. Hence, for the purpose of data archival where customers wish to limit the cost of storage, customers generally purchase inexpensive arrays. As there is no corresponding ASL for the uncertified arrays, some of the vital attributes, such as enclosure serial number, also known as array serial number, Vendor ID, Product ID, array name, SCSI version, used by the volume manager (VM) to manage fault tolerance across enclosure boundaries, is unavailable to the DMP process.
For arrays without ASL, the DMP views the arrays within a cabinet as a single block of storage (i.e., no granularity). Consequently, all the uncertified arrays connected to a host are configured into a single logical Just a Bunch Of Disks (JBOD) enclosure in DMP thereby compromising the fault tolerance characteristics of the SAN, which is undesirable. Particularly, in the absence of ASL, the DMP is unable to discover a unique enclosure connected to a host. Since the enclosure boundary is not recognized, multiple enclosures are categorized into one logical enclosure as JBOD. The volume manager is, thus, unable to place its configuration copies without compromising fault tolerance.
Accordingly, there is a need in the art for a method and apparatus for determining a disk array enclosure serial number within a SAN, especially when an ASL is unavailable.